This invention relates to active devices for multiplexing or switching optical signals in fiber optic systems, and specifically to a switchable coupler which selectively couples light from an input optical fiber to either of two output optical fibers.
Fiber optic multiplexing or switching in the past has been accomplished using passive frequency selective couplers, such as that described in U.S. Pat. No. 3,957,341, in which a pair of coupled waveguides have different phase propagation constants at all frequencies except for the frequency to be coupled, yielding a separation of this frequency from all other frequencies. Such systems require careful material selection for the desired frequency separation and do not lend themselves to adjustment during or after manufacture to accomplish the separation of optical signals over a broad range of frequencies.
In addition, fiber optic multiplexing has been accomplished using active systems in which a pair of waveguides are surrounded by a crystal material which has a voltage responsive refractive index. Such systems are difficult to manufacture and typically have a fairly narrow bandwidth of operation.
There exists, therefore, a need for a fiber optic switch which provides high resolution switching of a pair of inputs to a single output, or of inputs on a pair of separate optical fibers to a single optical fiber, in which the system is capable of switching a broad range of optical frequencies. Furthermore, there exists a need to provide such optical switching in a system which permits adjustment for the frequency to be switched after the system is manufactured and assembled. Furthermore, it is desirable that such switching be accomplished with the lowest possible throughput loss so that system efficiency will not be unduly limited by losses in the switching device.